Governing system for reheat turbine



NOV 5, 1957 M. A. EGGENBERGER GVERNING SYSTEM FOR mmm TURBINE Filed Aug. 24, 1956 United States Patent Gtifice 2,811,837 Patented Nov. 5, 1957 GovERNrNG SYSTEM PoR REHEAT TURBINE Markus A. Eggcnberger, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application August 24, 1956, Serial No. 606,020

4 Claims. (Cl. 60-73) This invention relates to elastic fluid turbine powerplants, particularly to a governing system for a large reheat type steam turbine plant receiving steam from a boiler that must be operated at or above a predetermined minimum ow.

In conventional large reheat type turbine powerplants, the control system includes, in addition to the main operating governor, a second pre-emergency governor" that controls a valve in the piping interconnecting the reheater and intermediate pressure turbines to intercept the ow of steam to the intermediate pressure turbines. The second governor closes the intercept valve on the occurrence of a pre-emergency condition to prevent the volume of steam trapped in the reheater and the interconnecting piping from expanding through the intermediate and low pressure turbines and creating a dangerous overspeed condition. This type of dual governing means has proven very satisfactory when the steam ow is provided by a boiler which can supply any quantity of steam required by the turbine at any time. ln systems of this type, the boiler supplies the required steam llow as controlled by the main governor in accordance with the speed or load requirements of the turbine, and the second or preemergency governor operates the intercept valve according to speed only, regardless of the position of the main control valves or the speed setting of the main governor. Thus, once the intercept valve is moved to the open position, it remains there unless the turbine shaft overspeeds to actuate the pre-emergency governor which, in turn, moves the intercept valve to the fully closed position if necessary.

However, when a boiler is used that requires a predetermined minimum steam flow through the boiler and reheater for safe operation, it would be necessary to throttle the ow of steam through the intercept valve when the minimum steam ilow at which the boiler will operate exceeds that required by the turbine downstream from the intercept valve. Such boilers are known as forcedcirculation boilers and are characterized by having pumps which continuously circulate water and steam over the heating surfaces and require a certain minimum rate of How to permit the proper amount of heat to be absorbed by the fluid. An example of such a forced-circulation boiler is one in which a flow of about 30% of the maximum ow rate is necessary for starting and a flow of about of maximum must be maintained upon large decrease in load if operation is to be continued, without risk of damage to the boiler. A system utilizing a boiler of this type must be capable of maintaining the minimum steam ow through the boiler and reheater when the turbine is shut down. It must provide for starting and synchronizing the turbine with a certain minimum reheat pressure without overheating any part of the turbine, and it must be capable of rejecting any amount of load and carry the remaining load under proper control while keeping the boiler flow at a level where operation of the boiler can be continued safely.

Accordingly, an object of this invention is to provide a control system for a large reheat type turbine powerplant using a forced-circulation boiler, which control system operates the main control and intercept valves to provide the proper steam flow to the turbines and disposes of any excess steam ilow by additional control means when the minimum safe boiler ow exceeds the turbine requirements.

A further object is to provide an improved governing system which positions the main control and intercept valves such that a substantially constant reheater discharge pressure is maintained when the steam flow is less than the minimum flow required for starting.

Another object is to provide a governing system of the type described in which a single speed-responsive device performs the dual function of controlling the intercept valve and the main control valves.

Other objects and advantages will become apparent from the following description, taken in connection with the accompanying drawing, in which the single ligure represents diagrammatically a large high temperature tandem compound reheat turbine powerplant with a governing system controlling steam How from a forcedcirculation" boiler.

Generally stated, the invention is practiced by providing a governing system having a single speed responsive device for simultaneously positioning the intercept valve and the main control valves when the steam ow from the boiler is below the rate necessary for starting, with special means for modifying the action of the linkage which connects the speed governor with the intercept valve so as to maintain that valve in wide open position when the steam ow rate exceeds that required for starting. The system also includes special means for bypassing that portion of the boiler llow which cannot be used in the turbine when the steam requirements of the turbine are below the minimum safe llow required by the boiler.

Referring now more particularly to the drawing, the invention is disclosed as applied to a compound reheat steam turbine powerplant having in series a forced circulation boiler 1, a superheater 2, a main emergency stop valve 3, main control valves 13, a high pressure turbine 4, a reheater S, a reheat stop valve 5c, an intercept valve 6, intermediate pressure turbine 7, low pressure turbine 8, a condenser 9, a feedwater heater 9b, and a boiler feed pump 10 for returning the lluid to the boiler. The turbines 4, 7, 8 may be on different axes, or may be coupled together on a common axis as shown. The conduits connecting these components have for convenience been labeled with reference numerals corresponding to the cornponent immediately upstream from the respective conduit sections. The high pressure turbine exhaust conduit 4a is provided with a non-return valve 4b. The boiler l is completely filled with liquid water before starting, and therefore a valve 2c and a high pressure Water separator 2e located in conduit 2g are provided for returning any liquid Water directly to the condenser 9 from the superheater when flow is established. The boiler stop valve 2d is closed when flow of liquid water is established, during starting, to prevent water from entering conduit 2a.

The valve 2c hereinafter referred to as the high pressure bypass valve, is an automatic pressure regulating valve of suitable design which can be forced open manually by a jack screw or the like (not shown). During start-up, this valve is manually opened to pass 30% of the rated How at some predetermined pressure. The boiler pressure is then increased by suitable controls which do not form a part of this invention; and when it reaches of rated boiler pressure, the pressure regulating mechanism of valve 2c, now controlled automatically by the boiler pressure, will open the valve to the proper position to maintain 105% of rated pressure in the superheater 2. When the turbine valves 13, 6 are opened and the steam flow is transferred to the turbine, the valve 2c will close slowly; and in normal operation, when the boiler pressure is at 100% of rated value, valve 2c will be held closed by its pressure-regulating mechanism (since, as noted above, it is set to open at 105% of rated pressure). If any abnormal operation, such as sudden loss of load, should cause the boiler pressure to increase to 105 the valve 2c will automatically reopen to bypass steam to the reheater through conduits 2b, 2g and thereby hold the boiler discharge pressure at valve 2d at 105% of rated value. The steam bypassed to the reheater is returned to the condenser through conduits 5a, 5b, and 5g.

In addition, an automatic valve 5d is provided for controlling the ow of excess steam through conduit 5g to condenser 9. This spillover valve 5d can be forced open manually by a jack screw or the like (not shown) and has a pressure controlling servo-mechanism (not shown) to bypass steam to the condenser 9 during the boiler starting period up to 30% load. Also, after the turbine is once started and has been operating above 30% load, this valve will automatically open to bypass steam in the event the turbine ow falls below the minimum safe ow for the boiler. Valve 5d is responsive to the pressure in conduit 5b through conduit 5e. After the turbine has been operating at high load and it drops down to between 10% and 30% load, the steam pressure in conduit 5a does not exceed the setting of the spillover valve 5d and therefore no steam is bypassed to the condenser. Below 10% load, the pressure in conduit 5b will exceed the pressure setting, whereupon valve 5d opens to bypass steam through conduit 5g to maintain a substantially constant reheater pressure. When the turbine is operating above 30% load, the pressure setting of valve 5d is automatically modified in accordance with the lirst stage pressure -of turbine 4 as detected by a suitable pressure detector 4c and transmitted through conduit 4d to hold the spillover valve 5d closed. To protect the apparatus from excessive temperature, desuperheaters 36 and 44 are provided in conduits 2f, Sg respectively to provide control of steam temperatures by automatically injecting water when the temperature rises above a preselected safe value. The desuperheaters 36, 44, boiler feed pump 10, feedwater heater 9b, and valves 2c, 2d, 5d are conventional types and their details are not important to an understanding of the present invention. This diagrammatic showing, of course, does not include many conventional elements of steam powerplants, the arrangement of which will be understood by those skilled in the art.

The primary means for regulating the rate of ow of motive lluid through the turbines is the high pressure inlet governing valve gear indicated diagrammatically at 13 as comprising a main flow control member 13a on a valve stem 13C. The governing valve member 13a is biased downwardly to closed position by a spring 13d engaging the upper end of valve stem 13C. The inlet valve is positioned in the opening direction by a rotatable cam 14 engaging a cam follower roller 15a carried at the extreme left-hand end of an operating lever 15, the righthand portion of which is fulcrumed at 15b on the valve casing. Cam 14 is positioned by rack and pinion 16, in a manner which will be obvious from the drawing. It is to be noted that movement of the rack to the right in the drawing causes the cam 14 to position valve stem 13C upwardly in the valve opening direction.

Actually, in large capacity steam turbines, the admission 0f motive uid to the high pressure turbine would ordinarily be controlled by a plurality of valves similar to that shown at 13, each having a main operating lever and a cam 14 keyed to a cam shaft but so shaped and oriented that the respective valves open in a preselected sequence. The inlet valve mechanism shown at 13 in the drawing is intended to represent that governing valve which opens first as the rack 16 moves to the right.

The means for actuating these multiple governing valves comprises a hydraulic motor 17 having a piston 17a slidably disposed in a housing 17b and connected by a bell crank 17e to position the rack and pinion 16. Motor 17 is controlled by a hydraulic pilot 18 having a slidable pilot member 18a connected to admit high pressure operating liquid to the upper end of cylinder 17b when the pilot member moves downwardly, and to the lower end of cylinder 17b when the pilot moves upwardly. The manner in which this is effected will be obvious from the drawing. It will, of course, be appreciated by those skilled in the art that the hydraulic pressure fluid for actuating the governing system is supplied by a suitable pump (not shown) which may for instance be driven from the turbine rotor. Pilot 18 is positioned by a oating lever 19, the right-hand end of which is connected by a link 20 to a double arm lever 21, one arm 21a being connected to link 20 and the second arm 2lb connected by another link 22 to piston 17a. Those familiar with the art will appreciate that motion of the main operating piston 17a produces a restoring effect on the pilot 18 by way of the followup linkage 22, 21, 20, 19.

In normal operation, pilot 18 is positioned by an operating governor shown generally at 23 as comprising a conventional centrifugal llyball governor connected to position a pivot 24 connected to an intermediate point of lever 25, the right-hand end of which is connected by link 26 to an intermediate point of lever 28. The right-hand end of lever 28 is connected to the left-hand end of floating lever 19 by link 30 and the left-hand end is connected to fulcrum 28a. The left-hand end of lever 25 is carried by an adjustable fulcrum member in the form of a nut 25a carried on a threaded synchronizing screw 27, the position of nut 25a being determined by suitable manual or remotely controlled motor means, represented diagrammatically by the hand wheel 27a. The ilyball governor 23 positions pilot 18 to move the piston 17a in order tu hold a preselected speed or load, the value of which is determined by the position of the synchronizing screw 27.

In the event of an emergency overspeed condition, conventional emergency governors (not shown) are provided for closing the main emergency stop valve 3 and certain other valves for shutting down the turbine. These emergency governors may be of any suitable mechanical or electrical type and are not material to an understanding of the present invention.

In the event of an emergency overspeed condition, it is also necessary in a reheat type turbine powerplant to stop the tlow into the intermediate pressure turbine 7 of the steam remaining in the high pressure turbine 4 and the comparatively long inter-connecting conduit 4a, reheater 5, and conduit 5a. The volume of the high pressure steam trapped in these components can be sutiicient to create a dangerous overspeed in the turbines if permitted to expand through the intermediate and low pressure turbines. Also, when a forcedcirculation boiler of the above-mentioned type is used, it is necessary to throttle the flow through conduit Sa when the requirements of turbine 7 are less than the minimum permissible ilow through the boiler. To accomplish these purposes, an intercept valve" 6 regulated in accordance with my invention is provided between conduits 5a, 6a. This valve is preferably located as close as possible to the inlet of turbine 7, rather than at a substantial distance from turbine 7 as might be inferred from the diagrammatic showing in the drawing.

A novel function of my improved control system is to simultaneously regulate the position of both the intercept valve and the main control valves in accordance with the setting of the single speed responsive governor 23 when the steam requirements of the intermediate pressure turbine 7 is less than the safe minimum ilow rate of thc boiler. Also, it is to be noted that in the event of overspeed, the governor 23 acts rapidly to close the intercept valves. Translating this operation to the boiler being used, the intercept valve 6 throttles the flow to turbine 7 until the flow rate reaches 30% of maximum boiler ow, which is the ow required for operating the boiler safely during start-up. Above 30% of maximum ow, the intercept valve 6 is in the wide open position and the steam pressure in conduit 5a is determined by the flow through the intermediate and low pressure turbines. However, after the turbine is started, the boiler control mechanism (not shown) is capable of following any load change down to 10% of normal rated ilow. It is to be noted that even though the boiler is capable of operating with steam ilow rates down to 10% of rated flow, the intercept valve 6 performs the essential function of maintaining a preselected substantially constant reheater pressure" in conduit 5a by throttling the flow to the turbine 7. The substantially constant reheater pressure provides for transferring steam ow from conduit 2b to 2a and conduit 5b to 5a while maintaining a smooth load response of the unit. A reheater pressure deviating appreciably from 30% of maximum reheat pressure would result in lluctuations which would be objectionable while transferring the steam tlow.

The intercept valve comprises a ow control member 6b positioned by a hydraulic motor 6c under the control of a pilot mechanism 6d. Pilot valve tif is connected to be positioned by a lever 6e, the right-hand end of which is connected through suitable linkage 6k, 6j, 6l to the piston rod 6i so as to effect restoring motion of the pilot 6j. The left-hand end of intercept pilot lever 6e is connected to link 40 which in turn is connected to the right-hand end of the piston head 41.

A pre-emergency relay 38 consisting of a hydraulic motor 38e located in chamber 38a and having a stem 38b connected to piston head 41 and a spring 38d biasing motor 38e in a downward direction is provided between hydraulic pilot 37 and pilot valve 6f. The function of relay 38 is to minimize the forces required from the speed governor to operate the pilot mechanism 6j. The tluid under pressure admitted to chamber 38a acts on the enlarged motor area 38e to operate the pilot f with only a minimum movement of governor 23 required. The travel of motor 38e positions intercept valve 6 between the fully open and closed position through the action of pilot valve f. The operation of relay 38 is controlled by the hydraulic pilot 37 through the action of a slidable pilot member 37a which is moved downwardly to drain the operating liquid from relay 3S and moves upwardly to admit operating liquid to the relay. ln the drawing, pilot 37 is shown above the on port or neutral position relative to conduit 43 connecting pilot 37 and relay 38, by a distance 37b, for reasons which will appear hereinafter. Pilot member 37a is connected to the midpoint of lever 31 and the left-hand end of lever 31 is connected to link 29 which is connected to lever 28. The movement of lever 28 is controlled by governor 23 through link 26 and lever 25 in the manner previously described.

The novel governing system further includes a restoring mechanism actuated by relay 38 which functions to restore pilot 37 to its on-port position after pilot 37 is moved by governor 23 to admit operating Huid to relay chamber 38a to open the intercept valves 6 in accordance with the increased load of the turbine to increase steam ow therethrough at substantially the same rate as the control valves until the intercept valve reaches its full open position. The restoring mechanism comprises a cam 3S positioned by a rack and pinion 34 connected to the left-hand end of head 41. The cam 3S is engaged by a cam follower roller 33a carried at the extreme right-hand end of lever 33. Lever 33 is pivoted about fulcrurn 42 and maintained in contact with cam 35 by tension spring 33b. Link 39 extending between an intermediate portion of lever 33 and the right-hand end of lever 31 transmits the movement of cam 35 to pilot valve stein 37a to produce a restoring effect on the pilot 37.

6 It may be noted that the upper lands of pilot members f, 37a are of an axial length essentially equal to the ports with which they cooperate, so that any movement thereof adjusts the opening of their cooperating ports.

It is to be further noted that movement of the rack downwardly in the drawing causes cam 35 to position pilot 37a in the upward direction to restore pilot 37 to its on-port position after pilot 37 has been moved downwardly by governor 23 to partially drain relay chamber 38a to move intercept valve 6 in the closing .irccton in accordance with decreased load of the turbine. It remains to note that, since the restoring mechanism is actuated by relay 38, when piston 38C reaches the end of its travel the cam restoring mechanism is disabled and pilot 37 is thereafter free to move solely in accordance with the movement of link 31 by governor 23 through linkage 25, 26, 28, 29.

lt will be appreciated that the linkage 29, 31, etc., for regulating the intercept valve 6 by the governor 23 may be made to operate in substantially the same manner if the pre-emergency relay 38 were omitted, in which case the cam restoring mechanism might be incorporated in the linkage 6e, 6j between the intercept valve 6 and the intercept pilot 6f.

For providing direct manual control of the turbine governing valves, as in starting the turbines, a manual starting member represented by hand wheel 32 is provided. This manual control is represented diagrammatically as comprising a threaded screw 32a carried in a stationary nut and having a lower end adapted to engage the righthand end of lever 25, so that by turning the hand wheel 32, pilot 18a can be forced downwardly through linkage 26, 28, 30, 19 to admit operating liquid to the upper end of cylinder 17 to move piston 17a downwardly in the valve closing direction. Handwheel 32 also forces pilot 37a downwardly through linkage 26, 28, 29, 31 to drain operating liquid from hydraulic motor 38 to permit spring 38d to bias piston 38e downwardly to move pilot 6d down to drain motor 6c and allow spring 6g to close intercept valve 6. In normal operation, the manually positioned screw 32a is backed completely away from the lever 25 (as shown in the drawing) so that the pilots 18a and 37a are under the sole control of the speed governor 23. In preparation for starting the turbine, the hand wheel 32 is turned to cause screw 32a to force pilots 18a and 37a to their lowermost positions, so that motor 17 will close the governing valve 13 and spring 6g will bias intercept valve 6 closed. Thus, when it is desired to admit steam through the valves 13 and 6, the screw 32a is gradually backed off, permitting pilot 18 to rise and cause motor 17 to open the control valves and pilot 37 to rise and admit operating fluid to relay chamber 38a to raise piston 33C, and pilot 6j to admit operating fluid to motor 6c and open intercept valve 6.

The operation of the entire system is as follows.

First, it is to be noted that the governing system as shown in the drawing represents the normal operating condition with the turbine operating about 30% of rated load. The 30% point" is the condition at which the steam flow of the boiler just equals the minimum flow rate required in the boiler during start-up, and is the point at which the intercept valve just reaches its fully open position. As indicated by the legend on the drawing, solid arrows indicate liuid ow as it occurs in normal operation, dot-dash arrows represent the ow during the starting cycle, below the "30% point, and other times when the minimum boiler flow exceeds the turbine requirements, and the dotted lines represent the paths of the condition sensing signals.

iNow, let it be assumed that the entire plant, including the steam generating apparatus 1, 2, 5 is shut down. The manual hand wheel 32 will be screwed down to depress link 26 and the main operating piston 17a and hydraulic motor 38e will be at the bottom of their stroke so that both valves 13a and 6b will be closed. To start the plant, the conventional turbine auxiliaries (not shown) for supplying lubricating oil to the bearings and hydraulic actuating liquid to the governor are put into operation and the boiler 1 is filled with water up to the boiler stop valve 2d (which is closed) and high pressure bypass valve 2c. Thirty percent llow rate through the boiler is then established at some preselected pressure, by running the boiler feed pump 10 and manually opening the valve 2c part way. The water is returned to the condenser 9 through the high pressure water separator 2e and conduit 2g. As soon as the fires in the boiler are lighted and steam is obtained in the water separator 2e, the steam ows through conduit 2g, 2f to the reheater 5 and is discharged to the condenser through conduits 5a, 5b, spillover valve Sd and conduit Sg. The spillover valve, which had previously been partially forced open, is now permitted to close by backing away the jack screw (not shown) to slowly build up the reheater discharge pressure in conduit 5a. At this time, all the turbine valves are closed. The fuel and air control means for the boiler (not shown) are now actuated to raise the boiler pressure and temperature until the superheater 2 is purged of all liquid water. Following this, the boiler and reheater pressure and temperature is built up and the high pressure bypass valve 2c starts controlling the superheater pressure at about 105% of rated pressure and spillover valve 5d starts controlling the reheater pressure at about 30% of full load reheat pressure. The main and reheat stop valves 3, 5c respectively are then opened.

The turbines may then be started and brought up to speed by rotating the hand wheel 32 so that pilot 18a is permitted to move upwardly and operating liquid is supplied to the lower end of hydraulic cylinder 17b to move piston 17a up and begin to open governing valve 13. Simultaneously with the opening of valve 13, pilot 37a is moved upwardly and operating liquid is supplied to hydraulic motor 38 which raises pilot valve 6f to admit uid to raise motor 6c to open intercept valve 6. The design of the conduits and valves is of course such that ow distribution through these valves provides the proper minimum steam ow for each turbine section 4, 7 to maintain desired temperatures therein. It is to be noted that before the turbine is started, the pilot 37 is in its lowermost position to open conduit 43 to drain so that there is no oil pressure acting on hydraulic motor 38, and the intercept valve remains closed since pilot 6d vents motor 6c to permit spring 6g to close valve 6. While this system has the valves 13, 6 arranged to open slightly when bringing the turbines up to speed, if desired this can also be accomplished by providing a governing valve pilot and lan intercept bypass valve, in a manner disclosed in my United States Patent 2,747,373, issued May 29, 1956.

When valves 13, 6 are opened suioiently to drive the turbine rotor at normal operating speeds, the hand wheel 32 can be backed off completely from lever 25 to permit governor 23 to control the speed of the turbine.

The turbine is now operating at normal rated speed. The electric generator (not shown) driven by the turbine rotor may now be synchronized and interconnected with the power distributing network (not shown). With load thus applied to the turbine rotor, the operating governor 23, up to the 30% point, simultaneously opens the control valve 13 and intercept valve 6 to increase steam ow substantially at the same rate through both valves.

Assuming a load increase, the speed governor 23 acts through linkage 2S, 26, 28, 30, and 19 to raise pilot 18u to admit operating fluid to motor 17 to further open control valve 13 and pilot 18 is restored to its on-port position by linkage 22, 21 and 20 after valve 13 is opened the required amount. Simultaneously, pilot 37 is raised through linkage 25, 26, 28, 29, 3l to admit operating liquid to relay 38 to raise piston 38e and piston 38C, in

turn, raises pilot 6i through head 41 linkage 40, 6e to admit liquid to motor 6c to open intercept valve 6. The upward movement of piston 38C acts through linkage 38b, head 41, rack and pinion 34, cam 35, roller 33a and linkage 33, 39, and 31 to restore pilot 37a to the 011-' port position where it covers conduit 43. At the same time, intercept pilot 6d is restored through linkage 6k. 6i, 6l.

Thus, with proper design of the foregoing mechanisms, the governor 23 controls intercept valve 6 and main control valves 13 to change the steam iiow to the intermediate and high pressure turbines simultaneously and at the same rate. This simultaneous control of both valves 6, 13 terminates at the 30% point," since at that load the intercept valve 6 is in its maximum open position. It can further be appreciated that the throttling of the in tercept valve between zero and 30% load maintains a substantially constant reheat pressure in conduit 5a, as is found necessary to obtain smooth load response of the unit.

It remains to note that upon further increase in load above the 30% point, the opening of control valve 13 is increased and the intercept valve 6 remains in the full open position, while pilot 37a continues to move up until at load it is in the position shown in the drawing, a distance identified 37b from the on-port" position. This over-travel 37b determines how quickly the intercept valve will close upon a sudden loss of load; and the effect of this relationship on the overall system is not important to an understanding of this invention. Other types of construction such as that disclosed in my application Serial No. 526,528, led August 4, 1955, could be utilized if this overtravel is considered undesirable.

When the load is increased above 30% of rated load, the reheat pressurel will increase, and in order to avoid having the spillover valve 5d reopen, a pressure signal from the high pressure turbine through conduit 4d resets the spillover valve pressure regulator (not shown) to a higher pressure in accordance with the first stage shell pressure, as measured by the pressure sensing device 4c. Upon decrease in load below the 30% point, governor 23 again effects simultaneous control of the intercept valve 6 and control valve gear 13 in the manner described.

As previously mentioned, after normal operation of the boiler is effected, the boiler controls (not shown) are capable of automatically regulating the boiler fuel and air supply down to 10% of the full load ow. During the period that the turbine is operating between 10% and 30% load, the reheat pressure remains substantially constant and the spillover valve which is set to bypass steam to the condenser when the steam How exceeds the amount required by the turbine remains closed. Below 10% load, which is the absolute minimum boiler ow for safe operation, the pressure in conduits 2b and 5b exceeds the pressure setting of valves 2c, 5d respectively and the excess steam will be bypassed to the condenser 9.

On sudden loss of load, the governor 23 moves pilot 18a downwardly to admit operating uid to the upper part of motor 17 to move valve 13 to the closed position, and simultaneously moves pilot 37a downwardly to drain fluid from chamber 38a to permit motor 38e to move downwardly to etfect closing of intercept valve 6. This action takes place within fractions of a second to prevent overspeed of the turbine. When this occurs, the high pressure bypass valve and the spillover valve open to bypass the excess steam tow to the condenser.

The invention provides a novel governing system for a reheat steam turbine powerplant in which a boiler requiring a predetermined minimum tlow for safe operation can be effectively used. The control system includes a bypassing arrangement for getting rid of the excess steam. This is accomplished by providing a single governor which simultaneously positions the control and in tercept valves whenever the required steam flow falls be- 2,s1 Les? low that required during the starting operation. The control and intercept valves admit steam to the respective turbine sections 4, 7 with the intercept valve so positioned as to maintain substantially constant pressure in the reheater 5, this constant pressure condition being required during the operation of transferring the ow of steam from the bypass conduit b to the turbine supply conduit 5a or vice versa. The linkages connecting the governor with the main control and intercept valves are designed so that, after the intercept valve is moved to the full open position, the control valves can be opened further to obtain maximum turbine loading.

While only one specific embodiment has been described herein, and that in quite diagrammatic fashion, it will be apparent that many changes and substitutions of equivalents may be made without departing from the invention. For example, While the boiler disclosed requires 30% of rated flow during starting, and a minimum ow equal to 10% of rated dow thereafter, and a minimum reheat pressure of 30% of full load reheat pressure, these figures are merely representative, since forced circulation boilers having other requirements may also be used.

The specific governor control system disclosed herein may be advantageously used in a reheat turbine power plant utilizing a conventional boiler, although it is especially valuable when used with the forced circulation type of boiler. It is, of course, intended to cover by the appended claims all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent in the United States is:

1. In governing mechanism for a reheat turbine powerplant having conduits connecting in series a steam generating means, a high pressure turbine, a reheater, a lower pressure turbine, and a condenser, the combination of first inlet valve means located between the steam generating means and the high pressure turbine for controlling the admission of steam to the high pressure turbine and having a range of operation from closed to a maximum open position corresponding to maximum turbine load, second intercept valve means located between the reheater and the lower pressure turbine for controlling steam flow to the lower pressure turbine from the reheater and having a range of operation from closed to a maximum open position corresponding to a preselected intermediate turbine load, the combination of a single governor responsive to turbine speed, first linkage means connecting the inlet valve means to said governor to position the inlet valve throughout the full operating range of the turbines, second linkage means connecting the intercept valve means to said governor to simultaneously open the intercept valve at a rate proportional to opening movement of the first valve means until the intercept valve reaches its maximum open position, said iirst and second linkage means being eiective to simultaneously position the iirst and second valve means in the valve-opening direction until the turbine is operating at said intermediate load condition, beyond which the first linkage continues to open the iirst valve while the second linkage maintains the second valve in maximum open position.

2. In a reheat turbine powerplant having conduits connecting in series a steam generating means, a high pressure turbine, a reheater, an intermediate pressure turbine, and condenser, the combination of a main control valve means located between the steam generating means and the high pressure turbine for controlling the admission of steam to the high pressure turbine and having a range of operation from closed to a maximum open position corresponding to maximum turbine load, an intercept valve located between the reheater and the lower pressure turbine for regulating the iiow between the reheater and the intermediate pressure turbine and having a range 0f operation from closed to a maximum open position corresponding to a preselected intermediate turbine load, a governor responsive to turbine speed, iirst linkage means connecting said control valves to the governor to position the control valves throughout the full operating range of the turbines, second linkage means connected to said first linkage means and said intercept valve to simultaneously open the intercept valve'at a rate proportional to opening movement of the main control valve means until the intercept valve reaches its maximum open position, and means for disabling said second linkage means While the iirst linkage means remains eiective to continue to open said first control valve means after the intercept valve has reached its maximum open position.

3. In a reheat turbine powerplant having conduits connecting in series a steam generating means, a high pressure turbine, a reheater, a lower pressure turbine, and a condenser, the combination of iirst inlet valve means 1ocated between the steam generating means and the high pressure turbine and having a range of operation from closed to a maximum open position corresponding to maximum turbine load for controlling the admission of steam to the high pressure turbine, second intercept valve means located between the reheater and the lower pressure turbine and having a range of operation from closed to a maximum open position corresponding to a preselected intermediate turbine load for controlling the iiow of steam from the reheater to the lower pressure turbine, a main operating governor responsive to turbine speed, rst control means connected between the iirst inlet valve means and control the main operating governor to position the inlet valve means throughout the full operating range of the turbines, second control means connected between the intercept valve means and governor to simultaneously regulate the intercept valve means in accordance with the operation of the governor at a rate proportional to the main valve means until the intercept valve reaches its maximum open position, said second control means including a hydraulic motor connected to the intercept valve, a pilot mechanism operated by the governor to control the hydraulic motor for positioning the intercept valve, and means operatively connected to said intercept valve and pilot mechanism to restore the pilot valve to its neutral position when the intercept valve has been opened a preselected amount and to disable said second motor means after the intercept valve reaches its maximum open position, whereby said governor may continue to operate said iirst motor means to move the inlet valve to the full open position after the intercept valve has reached its maximum open position.

4. In a reheat turbine powerplant having in series a boiler supplying a steam liow in excess of a predetermined minimum for safe operation, a superheater, a high pressure turbine, a reheater, an intermediate pressure turbine, and a condenser, the combination of a iirst conduit communicating between the superheater discharge and the high pressure turbine, first valve means in said iirst couduit having an operating range from closed to a maximum open position corresponding to maximum turbine load for controlling the admission of steam ilow to the high pressure turbine, second conduit means communicating between the reheater and the intermediate pressure turbine, a second intercept valve means in said second conduit having an operating range from closed to a maximum open position corresponding to a preselected intermediate turbine load for controlling steam iiow to the intermediate pressure turbine, governor control means responsive to turbine speed for regulating said first valve means through its operating range and simultaneously opening said second valve means at a rate proportional to the iirst valve means until the second valve means reaches its maximum open position and then to continue to open said iirst valve means, third conduit means con- 11 12 nesting between the superheager and ,reheatmg fourth com References Cited m the 61e of th1s patent duit means connecting between the Areheater and con- UNITED STATES PATENTS denser and third and fourth valve means in `said third and furth conduits respectively for bypassing excess leetet al' "Flggblg' boiler ow from the superheater and reheaxer to the e911- 5 ry denser when the turbine requirements are less than the FOREIGN PATENTS Hummm bon" HOW' 1,104,839 France June z2, 1955 

